Our goals are to understand whether the intrinsic ion-channel properties of auditory neurons shape their function. Specifically, we want to understand how some groups of Type I auditory neurons encode low- intensity sounds whereas others encode high-intensity sounds. The mechanisms shaping these response features are unknown but are likely to rely on both pre- and post-synaptic specializations. Recordings from the isolated somata of auditory neurons suggest that diversity in ion channel properties may influence their response, but a clear correlation has not been demonstrated. To directly make such correlations, we propose to use semi-intact in vitro preparations of rat cochleae that preserve the anatomical and functional connections between the spiral ganglion and organ of Corti. The approach brings together whole-cell patch-clamp recordings, neuronal labeling, morphometric analysis, and computational modeling to explore how the biophysical properties intrinsic to primary auditory afferent neurons shape their physiological responses. Furthermore, because our experiments are from animals at ages before and after the onset of hearing, we can characterize the time course over which Type I auditory neurons' mature biophysically and morphologically into distinct functional groups.